The invention concerns a method for preheating melt-goods, i.e., materials to be molten, consisting of glass fragments and glass batching or such bulk goods, using a heating gas, wherein the melt-goods are vertically descending by gravity in a plurality of small columns and are preheated by heating-gas flowing in the opposite direction in the process of indirect heat-exchange, the temperature of the melt-goods columns increasing from the top toward the bottom whereas the temperature of the heating-gas flow gradually decreases from the bottom toward the top. The invention concerns also a plate heat-exchanger to carry out the method.
The German patent documents Nos. 32 17 414 C1 and 37 16 687 C1 disclose equipment, i.e., plate heat-exchangers, for carrying out the above stated method. Such known equipment operates in a problem-free manner as long as the bulk-goods to be preheated are dry, as in that case they will easily descend by gravity through the ducts of the equipment or plate heat-exchanger, without adhesion, caking or lastly clogging bridge-formation coming into being. This is also the case to some extent for broken glass when moist because enough hollows will form between the glass fragments to allow the steam generated during preheating to escape through the top of the equipment or plate heat-exchanger. If however the bulk or melt-goods to be preheated are moist glass fragments and moist or dry glass batching, and this shall be the rule, the above methods do fail. In such instances the dreaded adhesions and bridge-formations arise in the plate heat-exchanger and the downward flow of the goods to be preheated is interrupted, i.e., blocked. One of the reasons for such phenomena is steam produced from the basic moisture of the glass batching generated when heating this glass batching to above 100.degree. C., i.e., when it is being preheated. Lastly the water of crystallization in the soda portion of the glass batching contributes to the generation of steam in the course of this preheating. Because evaporation only starts at a depth between about 1 and 2 m when preheating such bulk goods, then when charging broken glass and glass batching the steam no longer can escape upwardly from the charged material because latter acts like a stopper. As already mentioned, because of the steam condensing in the ducts of the plate heat-exchanger, bridges may be formed and hence blocking may arise. Known solutions to this problem are mechanically complex and expensive.
The German patent document No. 40 00 358 A1 discloses a method and a heat-exchanger for drying and pre-heating a melt-good consisting of glass fragments and glass batching, where one or only a few columns of the melt-good descending by gravity are transversely crossed by the heating gas: contrary to the initially cited method, this signifies direct contact with the heating gas. The steam so generated is evacuated laterally together with the flow of heating gas used for drying and preheating, without the steam condensing. However this method is not immediately applicable when a larger number of melt-good columns are involved which are hermetically sealed laterally and, because of gravity, migrate from top to the bottom and in the process are preheated by heating gas flowing in the opposite direction and (indirectly) by means of heat-exchange surfaces. An upper introduction means for the melt-good to be preheated is not heated and therefore is unutilized for drying, only enlarging the equipment height. However when the input material is moist, steam already may form in the transition zone between this introduction means and the preheating segment of this known equipment: it may condense and cause clogging.